Imagine a camera, no larger than existing digital cameras, that can directly find depth edges or create stylized images. As we know, a flash to the left of a camera creates a sliver of shadow to the right of each silhouette (depth discontinuity) in the image. We add a flash on the right, which creates a sliver of shadow to the left of each silhouette, a flash to the top and bottom. By observing the shadows, one can robustly find all the pixels corresponding to shape boundaries (depth discontinuities). This is a strikingly simple way of calculating depth edges. Below, we show one potential application in generating NPR images.

Watch a short movie (12MB).

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Hence, after developing this technique in 2002, we discussed with various researchers at CVPR 2003 (where it was also shown as a demo), ICCV 2003 and Siggraph 2003 (where the basic ideas of depth edge detected were presented as a sketch) and asked for feedback. We concluded that, one possible reason this type of strategic placement of light sources very close to the camera was overlooked is that, in-fact for most photometric stereo or shape-from-shadow or shape-from-shading technique, the flash configuration is a failure case. However, beyond our search and discussion with researchers, it is quite possible that a approach similar to ours was explored in 60's or 70's. So we asked researchers who have been active since 70's who refered us to papers that analyzed intensity edges in images but those techniques required widely varying illumination on objects with uniform albedo.

For most techniques to compare with, a simple question to ask is : Will the method find a depth edge for a white piece of paper in front of a white background ?

Here is what Stan Birchfield (Ph.D. Thesis 'Depth and Motion Discontinuities', Stanford University, 1999) has to say about our work (printed with permission).

"Detecting depth discontinuities is fundamental to image understanding, and important for many tasks.  With a well-crafted hardware modification, this work has moved this problem from theoretical possibility to practical reality.  The results are orders of magnitude better than anything previous."

If you are familiar with related techniques, we would love to hear from you.